The present invention is directed to a magneto-optical measuring transducer which is utilizing in measuring high currents at high voltages by rotating the direction of polarization of a polarized beam in response to a magnetic field created by the current to be measured.
Magneto-optical measuring transducers are known. An example of a known transducer is disclosed in German Auslegungsschrift 1,283,363. In this reference, polarized light is passed through a Faraday rotator which is arranged in a magnetic field whose strength is dependent upon the current to be measured. The direction of polarization of the polarized light will be rotated with the amount of rotation being dependent upon the magnetic field so that the polarized light emerging from the rotator has its polarization direction altered. After emerging from the rotator the light is passed through a second Faraday rotator which is at earth potential. An auxiliary circuit imparts a controllable magnetic field to the second rotator to rotate the direction of polarization of the beam back to the original polarization direction. The strength of the auziliary current which is used to create the controllable magnetic field is thus a gauge for the strength of the current which is being measured by the first rotator.
Measuring transducers of this type can exhibit a relatively high degree of accuracy of measurement in the range of the normal or nominal currents, i.e. the current strengths for which the system is designed. However, in the case of an overload, excessive currents can occur at such a magnitude that they do not fall within the measurement range of one transducer. In order to measure the magnitude of these excessively high currents, it has been necessary to provide a second measuring transducer and consequently it was necessary to accept a very high construction cost for producing a measurement device.